The present invention relates generally to the field of automatically tuned stringed instruments and, more particularly, to an automatically tuned guitar.
A number of tuning systems to automatically tune a musical instrument have been proposed. Skinn et al., in U.S. Pat. Nos. 4,803,908 and 4,909,126, teaches a tuning system that is broadly applicable to stringed and brass instruments. The system detects musical tones and produces a blended signal which is converted to a digital signal. The digital signal is converted to a frequency signal which is compared to a predetermined frequency value to produce an electrical signal which actuates a motor to perform the tuning function. However, the system of Skinn et al. makes no allowance for distinguishing the vibration of one string from that of an adjacent string. This presents the potential for pitch confusion where a plurality of adjacent string work in coordination with a pitch detection device. This may be referred to as "inter-pickup crosstalk."
For example, imagine tuning a guitar's fifth string from a completely loose condition to it standard pitch of 440 Hz. To get to that frequency, the frequency of the string must first pass through 330 Hz, the standard frequency of the sixth string. If the pickup for the sixth string detects this frequency, it will falsely actuate the tuning channel for the sixth string.
Thus, there remains a need for an automatic tuning system for a stringed musical instrument in which there is a dedicated pickup for each string of the instrument. The system must also be able to accurately distinguish precisely which string is being strummed or which string of a plurality of strings is to be tuned by the system. Such a system should eliminate inter-pickup crosstalk.
Another problem in the prior art lies in its inability to distinguish enharmonic fretted tones. In other words, a guitar is normally manually tuned by depressing a string a number frets up from the bridge and comparing its tone with that of the next higher string on the instrument. The tautness of the string is adjusted and its adjusted tone is again compared to that of the adjacent string. This is repeated until the strings have the same tone and the process is repeated until all of the strings are in tune.
In the prior art, no provision is made to prevent pickups other than the one for a specific string from picking up the tone from an adjacent string and begin adjusting the tension on the wrong string. As used herein, the term "fretted string" refers to a string that is depressed against a fret. Prior art systems failed to recognize the problem of distinguishing tones from adjacent fretted strings. Thus, there remains a need for an automatic tuning system that will only tune a string in response to a tone detected from that string. Such a system should also eliminate the effect of one string's vibration on the field of all adjacent pickups.
The prior art's claims of automatic tuning are automatic in the sense that, once one has wound the string manually to a frequency close to that desired, the string tensioning apparatus in coordination with a pitch detector will maintain a certain tufting. The prior art docs not coordinate the degrees of pitch increase with the fixed step nature of the motor. Kurtz, U.S. Pat. No. 5,009,142, recognized the problem associated with string strain effect on tension and pitch increase but offers a solution that involves manual winding. Skinn incorporated a linear actuated motor as a means for string winding but this method is also manual to a point. This method does not take into account that, on one string, string tension yields different rates of pitch increase. Thus, the fixed degrees of a stepper motor may not be in sync with the desired frequency. The fixed gear steps driven by a stepper motor must synchronize with a predetermined set of pitch steps. If the steps of the stepper motor are not coordinated with desired steps of pitch, reaching a desired pitch is a matter of pure luck. In order to know what a gear step will produce in terms of pitch increase or decrease, the system must factor in the pulse train signal to the stepper motor, reduction gear output, dimensions of the tuning apparatus, string tension, and specific frequency ranges in which the system is activated and deactivated.
An automatic tuning system for a stringed musical instrument should also provide a "dead zone" at predetermined gear steps before and after a desired pitch for each string. A dead zone permits the string to go slightly out of tune before being automatically retuned. This feature keeps the strings most nearly in tune and prevents "hunting" in which the system constantly tunes to find the exact desired frequency.
Such a system should also provide an easy means to install new strings and remove old or broken strings. The system should provide a simple to use guide which directs the strings into the tuning apparatus without difficulty.